Extract, transform, and load (ETL) refers to a process in data warehousing in which data from source systems are loaded into a data warehouse. The extracting step involves extracting data of interest from source systems so the data can be further processed. The transforming step typically involves converting data into a standardized format and validating the data. The transforming step may also involve aggregating data. The loading step involves loading the transformed data into a target system (e.g., into a target database).